A Splash of Memories

Eir used to love the fictional stories her grandma tells him everytime he visit her however, one day her grandma passed away. Now Eir is in 1st year of highschool and he no longer believes in the stories her grandma used to tell him however, this mindset of his was changed by a school trip. What could have happened in that school trip? Will Eir be able to keep up with what he discovered in that school trip?